Imaging of lithographic plates by gelatin transfer



Nov. 25, 1969 R. L. ORANSKY ET L 3,480,432

I IMAGING OF LITHOG-RAPHIC PLATES BY GELATIN TRANSFER Filed Oct. 20, 1967 PLACE GELATIN NEGATIVE PAPER AND ORIGINAL IN FACE-TO-FACE CONTACT IMAGE BY EXPOSING TO LIGHT I3 SEPARATE DEVELOPE GELATINE NEGATIVE PLACE GELATI NEGATIVE AND MASTER IN FACE-TO-FACE CONTACT TRANSFERRING IMAGES TO MASTER SEPARATE IMMERSE MASTER IN TANNING SOLUTION SQUEEGEE INVENTORS RAYMOND L. ORANSKY RICHA RD H. ROMBALSKI jiuMelL,

United States Patent U.S. CI. 96-28 Claims ABSTRACT OF THE DISCLOSURE A process of readying a paper lithographic master for use on an offset duplicator comprising imaging a planographic master by contact transfer of gelatin silver-halide emulsion images thereto, passing the imaged master through a tanning solution and thoroughly wetting both sides thereof and hardening said images, and removing excess tanning solution from said surfaces, said master being flexible enough to withstand bending in the dry state into a 180%. inch are without damage and being composed of (1) a paper web machine coated on at least one side (2) semi-barrier coatings on both sides, having a Cobb water absorption value in the range of 0.04 to 0.15 (grams/100 sq. cm.-120 seconds) and composed of a flexible water-insoluble pigmented cured latex and (3) a top planographic coating on the machine coated side composed of a hydrophilic water-insoluble binder, an oil-obsorptive paper-coating-grade mineral pigment and colloidal silica, said master after transfer and treatment with said tanning solution exhibiting no more than a momentary tendency to curl.

RELATIONSHIP TO OTHER APPLICATIONS The present application is a continuation-in-part of our copending application, Ser. No. 518,622, filed Jan. 4, 1966, now abandoned, and entitled Imaging of Lithographic Plates by Gelatin Transfer.

This invention is concerned with the readying of a lithographic master of special construction for use in an offset duplicator, and apparatus therefor.

It is known to reproduce printed and the like matter photomechanically by exposing a silver halide gelatin negative paper to light while the face of the negative paper is in contact with a suitable original, followed by hardening the background areas and contact transfer of the gelatin in the imaged areas to a suitable receptor sheet. The imges are then hardened with a tanning agent. See US. Patent Nos. 2,596,756; 2,675,313 and 2,865,745. Several commercial desk type copiers embody this principle, e.g. the Verifax, Readyprint and Ektalith Copiers. This process can be used for imaging planographic masters, but if the machines are used without special adapters a lightweight flexible master must be used. However, the tanning of the images causes a lightweight master to curl severely, so much so that it is extremely difficult to position the master on the press.

This curling problem has been overcome in the past when imaging in this manner by using masters developed for long press runs in the order of thousands of copies. These masters have a heavier body stock with a barrier base coating that prevents any penetration of water into the body stock. Such masters are undesirably more expensive, roughly twice that of the master used in this invention, which makes them uneconomical for short runs of under 500 copies or so. In addition, because of their heavier thicker coatings, they are relatively inflexible and 31,480,432 Patented Nov. 25, 1969 ice cannot be processed in the common copiers but must be specially handled in adapting equipment.

The present invention overcomes these and other problems through the use of a special lightweight low-cost master in combination with a certain sequence of processmg steps. The imaged master, when ready for the press, has no tendency to curl.

This method of preparing a plate permits the use of common copiers for imaging and is so simple and reliable that on numerous occasions plates have been prepared and placed on the press producing satisfactory copies in a normal manner within 60 seconds from the time of the insertion of the positive original into the copier.

The drawing attached to and forming a part of this specification schematically illustrates the steps of the present process. As shown at 11, the gelatin-silver halide negative paper is brought in face-to-face contact with an original. The composite is then exposed at 12 to light from the back side of the gelatin negative paper, followed by separation of the sheets at 13. The gelatin negative paper is developed by contact with an activator solution at 14, causing reduction of the silver halide in the background areas and hardening the gelatin, while leaving the image areas tacky and mobile. The gelatin negative paper is then brought at 15 into contact with the surface of the planographic plate and a portion of the gelatin in the image area is transferred to the surface of the plate. This is followed by separation at 16 of the plate and the gelatin negative paper.

Steps 11 through 16 are automatically carried out in the present-day copiers and need not be further described.

In accordance with this invention, the imaged plate at 17 is immersed in a conventional tanning solution so that both sides of it are thoroughly wet and the image areas are hardened. This is followed by squeegeeing of the plate at 18 to remove excess tanning solution. The plate will then exhibit no more than a momentary tendency to curl and in 20 or 30 seconds will be found to lie flat and be ready for placing on the press.

One of the present inventors participated in the development of a low-cost flexible paper lithographic plate, particularly designed for use in the encoding of checks with magnetic ink, as described in US. Patent No. 3,160,093. The present master is the same as that described in the patent, all of the teachings of which are hereby incorporated by a reference, with the exception that a different planographic top coating is used because the one described in the patent is not receptive to imaging with a gelatin-silver halide emulsion.

One of the characteristics of this master is that the barrier coating is made tohave a controlled water resistance, as measured by the Cobb test, both to prevent the development of objectionable curl following the transfer step and the development step, and also to promote good bonding between the top coat and the barrier coat, thus permitting a less expensive and more flexible coating and procedure to be used. This master is flexible enough to withstand bending into a l- A inch are from either direction without damage to the planographic coating.

The present master consists of a paper web of preferably 50-70 lbs. ream weight machine-coated on at least one side with semi-barrier coatings on both sides and a top planographic coating on the machine-coated side. The barrier coatings have a Cobb water absorption value in the range of 0.04 to 0.15 (grams/ sq. cm.-l20 seconds) and consist of a flexible water-insoluble cured pigmented latex such as an acrylic latex. The top planographic coating consists of a hydrophilic water-insoluble binder, an oil-absorbent paper-coating-grade mineral pigment, and colloidal silica to improve retention of the transferred gelatin. It is applied preferably in an amount in the range of 5 to 8 lbs. per ream.

The term oil-absorptive paper-coating grade mineral pigment as employed in the present specification designates those paper-coating-grade mineral pigments known to the skilled in the art to be oil absorbent and includes various pigments such as clay, talc, blanc fixe and titanium dioxide.

In a preferred lithographic master for use in the process of the present invention, titanium dioxide is employed as the oil absorbent paper-coating-grade pigment. Masters containing titanium dioxide as the pigment give clean copies from the start when employed in lithographic processes. Whereas, when clay is employed as the pigment the first 5 to 20 copies made from the master often show toning. Therefore, as it is desirable, particularly in short runs, to avoid loss of early sheets due to toning, the masters containing titanium dioxide as the oil absorbent paper-coating-grade pigment are preferred.

The coatings employed as the planographic top coa for the lithographic masters employed in the process of the present invention are prepared in accordance with conventional procedures. The various components of the coating are generally prepared individually and then admixed in accordance with known procedures. In a representative procedure, a pigment slurry is prepared by grinding the dry pigment with water to produce an aqueous suspension having the desired pigment content. In some cases, a small amount (about 2 percent by weight based upon the amount of pigment) of polyvinyl alcohol is added to the water in which the pigment is to be suspended.

An aqueous suspension of colloidal silica is prepared by suspending colloidal silica, with stirring, in water. When titanium dioxide is employed as the pigment the colloidal silica is preferably employed at a concentration of from about 10 to about 18 parts by weight with respect to the titanium dioxide.

In some cases, it may be desirable to employ an antifoam agent or a dispersing agent or both in the coating to depress the tendency of the coating to foam and/or to aid in the even spread of coating layer on the paper base. The particular antifoam agent or wetting agent to be employed is not critical. The antifoam agents and dispersing agents conventionally employed in the paper coating art are acceptable. In a convenient procedure, tributyl phosphate (5 parts by weight) and 4 nonylphenylpolyoxyethylene glycol (2 /2 parts by weight) are dispersed in water (92 /2 parts by weight) and the resulting aqueous dispersion added to the coating composition.

Furthermore, a small amount of dye can be added to the planographic coating composition to indicate the side of the master containing said coating. In another embodiment, thiourea can be employed in the planographic coating to darken the silver halide emulsion on transfer.

In the preparation of the coating compositions, the pigment suspensions, colloidal silica suspensions and other components such as antifoaming agents, dispersing or wetting agents or dyes are dispersed, with stirring, in a hydrophilic water-insoluble binder such as the polyvinyl alcohol type adhesives. The adhesive is generally dispersed in warm water with stirring and the other components of coating are added to the hinder or adhesive solution. Following the addition and mixing of the components, additional water is added to the mixture to bring the solid contents of the coating composition to between about to about 25 percent by weight.

The Coatings A, B, C and D set forth in Table I were all prepared by adding, with stirring, the aqueous pigment suspension, the aqueous colloidal silica suspension, and the other components such as the dye and the antifoam and dispersing agents to an aqueous solution of the polyvinyl alcohol. Following the addition of the various components to the polyvinyl alcohol solution, the mixture thus formed was stirred until it became uniform. Stirring was continued and additional water added to the coating to bring the coating to the desired concentration of solids. Coatings A, B, C and D are all comprised of about 19 percent solids. In the following table all percentages are by weight.

The following examples are merely illustrative and are not to be construed as limiting the scope of the invention.

TABLE I Coating A Parts by wt. of component Coating components: in coating Clay (English coating clay) (aqueous slurry- 60 percent clay) 142 Colloidal silica 1 (aqueous suspension8 percent silica) 188 Binder, polyvinyl alcohol 2 (aqueous solution 10 percent polyvinyl alcohol) 200 Thiourea (8.3 percent aqueous solution) 36 Patent blue 2Y dye (1 percent aqueous solution) 0.222

Coating B English coating clay (aqueous slurry-60 percent clay) 137 Colloidal silica 1 (aqueous suspension8 percent silica) 225 Polyvinyl alcohol 2 (aqueous solution-10 percent polyvinyl alcohol) 240 Tributyl phophate (5 percent) and 8 nonylphenylpolyoxyethylene glycol (2 /2 percent) in water 10 Patent blue 2Y dye (1 percent aqueous solution) 3 Coating C TiO (aqueous slurry62.5 percent TiO 131 Colloidal silica 1 (aqueous suspension8 percent silica) 225 Polyvinyl alcohol 2 (aqueous solution-10 percent polyvinyl alcohol) 240 Tributyl phosphate (5 percent) and 8nonylphenylpolyoxyethylene glycol (2 /2 percent) in water 10 Patent blue 2Y dye (1 percent aqueous solution) 3 Coating D TiO; 3 (aqueous slurry-62.5 percent TiO by weight) 139 Colloidal silica (aqueous suspension8 percent silica by weight) 175 Polyvinyl alcohol (aqueous solution-10 percent polyvinyl alcohol) 240 Tributyl phosphate (5 percent) and 8-nonylphenylpolyoxyethylene glycol (2 percent) in water 10 Patent blue 2Y dye (1 percent aqueous solution) 3 1 Cnbosil M-5 sold by Cabot Corporation.

Vinol 125 sold by Air Reduction Chemical Co.

3 Slurry contains polyvinyl alcohol in an amount equivalent to 2 percent of TiO Planographic masters were prepared by applying each of the coatings of Table I to a paper stock as the sole planographic coating. The paper stock was composed of equal amounts of long fibers and short fibers and contained from 6 to 8 percent mineral filler. The paper stock was sized with rosin and alum and weighed about 52 pounds per ream (500 sheets-25" x 38"). One side of the paper was base-coated at the rate of 4 pounds/ ream with a coating comprised of clay parts), casein (20 parts) and dimethylol urea (2 parts). Following the application of the base coating both sides of the paper stock were given a barrier coat comprised of acrylic latex (2 parts), clay (1 part), melamineformaldehyde resin /2 part). The barrier coat was applied to each side at a rate of 5-6 pounds per ream and was then dried and calendered.

Coating A was applied by means of an air knife coater to the base-coated side of the master paper stock in an amount sufficient to provide 6.0 pounds of coating per ream. The coated sheets were then dried in a forced air oven at 290 F. for 25 seconds. Thereafter, the dried sheets were cured in a convection oven at a temperature of 600 F. for seven seconds.

Coatings B, C and D were each applied individually to the base coated side of the stock paper as the only planographic coating. Each coating was applied by means of an air knife coater in an amount sufficient to 6.0 pounds of coating per ream of paper. The coated sheets were dried in forced hot air (300 F. for 45 seconds) and the dried sheets cured in a convection oven for three minutes at 275 C. The cured sheets were then calendered on a stack having four nips, e'ach nip having a pressure of 1,100 pounds per linear inch.

The masters thus prepared were imaged with an Eastman Kodak Company Readyprint Copier, Model No. 1, using that companys Readyprint Negative Paper R and Activator Type R. This was followed by immersing the master in a tanning solution containing tannic acid at a pH of about 1.5. The plate was then squeegeed and within 20 or 30 seconds was placed on an offset duplicator (Multilith, Model 1250), treated with an aqueous solution of glycerin and mono-ammonium phosphate (Playtex) and then used for duplicating 500 copies. Masters bearing coating A, B, C or D as the sole planographic coating each gave 500 satisfactory copies without toning.

In a further example, sheets of the masters bearing Coating B and master bearing Coating C were cured in the convection oven at 275 C. for an additional 5 minutes. Following the extra heating period, the masters were imaged, tanned, squeegeed and placed on a duplicator as previously described. When the masters so prepared were placed on a duplicating machine the master containing clay as the pigment in the planographic top coat toned for the first copies. The masters containing TiO as the pigment in the planographic top coating did not exhibit toning and the copies made therefrom were clean from the start.

One principal advantage of this invention is that it permits a simple, integral unit to be used to image the masters. All that is required is the addition to existing copiers of guide means for directing the plate, after separation from the gelatin imaging sheet and immersion in the activator solution through a tank of the tanning solution followed immediately by two rotating squeegee rolls for removing excess solution. These additions can be made integral with the copier, with a simple switch being used to direct ordinary copies out of the machine in normal use.

The apparatus contemplated for use in this invention can be described as means for imaging a planographic master with a positive image of an unhardened gelatinsilver halide emulsion, means in direct sequence wherewith for passing said master through an aqueous tanning solution and thoroughly wetting both sides followed by means for squeegeeing both sides of said master to remove excess tanning solution therefrom.

Having described this invention, what is sought to be protected by Letters Patent is succinctly set forth in the following claims:

1. A process of readying a paper lithographic master for use in an offset duplicator comprising imaging a planographic master by contact transfer of gelatin silver-halide emulsion images thereto, passing the imaged master through a tanning solution and thoroughly wetting both sides thereof and hardening said images, and removing excess tanning solution from said surfaces, said master being flexible enough to withstand bending in the dry state into a 1"80- A inch are without damage and being composed of (1) a paper web machine coated on at least one side, (2) semi-barrier coatings on both sides, having a Cobb water absorption value in the range of 0.04 to 0.15 (grams/ sq. cm.1.20 seconds) and composed of a flexible water-insoluble pigmented cured latex and (3) a top planographic coating on the machine coated side composed of a hydrophilic water-insoluble binder, an oil-absorptive paper-coating-grade mineral pigment and colloidal silica, said master after transfer and treatment with said tanning solution exhibiting no more than a momentary tendency to curl.

2. Process of claim 1 wherein said paper web has a ream weight in the range of 50 to 70 pounds, wherein said hydrophilic water-insoluble binder is a cured polyvinyl alcohol, and wherein the coating weight of said top planographic coating is in the range of 5 to 8 pounds per ream.

3. The process of claim 1 wherein the lithographic master bears a planographic coating having an oil-absorptive paper-coating grade pigment consisting of titanium dioxide and a hydrophilic water-insoluble binder consisting of polyvinyl alcohol.

References Cited UNITED STATES PATENTS 2,714,066 7/1955 Jewett et al 96-86 XR 2,805,159 9/1957 Unkauf 9675 2,534,650 12/1950 Worthen 101-149.2 2,704,712 3/1955 Jackoun 9628 XR 3,091,531 5/1963 Callear et al 9628 XR 3,160,093 1.2/1964 McCrum et al. 117-86 XR GEORGE E. LESMES, Primary Examiner B. BETTIS, Assistant Examiner US. Cl. X.R. 

